US7638941B2 - Lamp with multi-colored OLED elements - Google Patents

Abstract

Solid-state area illumination stems and method for forming such systems are provided. The illumination system comprises: a plurality of OLED devices each device formed on a separate substrate and each device emitting light at a plurality of angles relative to the substrate, the emitted light having different ranges of frequencies at different ranges of the plurality of angles; and a support positioning each of the plurality of OLED devices at a plurality of orientations relative to an area of illumination, the positioning being defined so that any point on any surface within the area of illumination will receive a broadband combination of light from more than one of the OLED devices.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned, co-pending patent application U.S. Application Publication Nos. 2004/0149984 entitled COLOR OLED DISPLAY WITH IMPROVED EMISSION filed Jan. 31, 2003 in the names of Tyan et al.; U.S. 2004/0140757 entitled MICROCAVITY OLED DEVICES filed Jan. 17, 2003 in the names of Tyan et al.; U.S. 2005/0073228 entitled WHITE-EMITTING MICROCAVITY OLED DEVICE filed Oct. 7, 2003 in the names Tyan et al.; and U.S. Pat. No. 6,917,159 entitled MICROCAVITY OLED DEVICE filed Aug. 14, 2003 in the names of Tyan et al.

FIELD OF THE INVENTION

The present invention relates to the use of organic light emitting diodes for area illumination, and more particularly to broadband illumination using colored light emitters.

BACKGROUND OF THE INVENTION

Solid-state lighting devices made of light emitting diodes (LEDs) are increasingly useful for applications requiring robustness and long-life. For example, solid-state LEDs are found today in automotive applications. These devices are typically formed by combining multiple, small LED devices providing a point light source into a single module together with glass lenses or reflectors suitably designed to direct the light as is desired for a particular application; see for example, WO99/57945, published Nov. 11, 1999. These multiple devices are expensive and complex to manufacture and integrate into single illumination devices. Moreover, point sources of light such as LEDs or incandescent lamps tend to require additional light diffusers, e.g. lampshades, to avoid glare.

Organic light emitting diodes (OLEDs) are manufactured by depositing organic semiconductor materials between electrodes on a substrate. This process enables the creation of area-emitting light sources having an extended light emitting surface area on a single substrate, thereby reducing glare and improving the efficiency of illumination. The prior art describes the use of one or more OLEDs in lighting, for example U.S. Pat. No. 6,565,231, entitled OLED Area Illumination Lighting Apparatus filed by Cok on May 28, 2002. In particular, the use of specially constructed layers within an OLED device to form optical cavities that can enhance the amount of light output from an OLED device is known. For example, U.S. Application Publication No. 2004/0155576 filed Feb. 4, 2004, entitled “Microcavity OLED Devices” describes such an OLED device. Other means, such as diffraction gratings can be employed to similar effect. Because these layers in these devices provide an optical filtering effect, the layers are carefully selected to minimize frequency dependence on the angle of emission for the emitted light. Alternatively, scattering or diffusing elements are employed to maintain a consistent color of light emitted over the surface of the OLED device and at any viewed angle.

It will be appreciated that these techniques involve filtering, reflecting or otherwise processing light generated by the OLED device and that with each such processing step, a portion of the light generated by the OLED device can be subject to optical losses thus, the overall efficiency of such an illumination system as measured in terms of lumens per watt of supplied energy may decrease. It will further be appreciated that the efficiency of an area illumination system can be a critical feature in the selection of one form of area illumination as compared against other potential forms of area illumination, particularly, where vast areas such as roadways, athletic stadiums, or other areas are to be illuminated.

Another critical factor in the selection of an area illumination system is the aesthetic appeal or lack thereof of the selected area illumination system itself. Colored lights are sometimes employed as decoration or specialty lighting, for example as holiday lighting. Colored illumination is typically provided using filters over white-light lamps. See for example, US 2004/0090787 entitled “Methods and Systems for Illuminating Environments” published May 13, 2004; US 2004/0052076 entitled “Controlled Lighting Methods and Apparatus” published Mar. 18, 2004; and US 2004/0105264 “Multiple Light-Source Illuminating System”, published Jun. 3, 2004. However, it will be appreciated that here too, the filters absorb light, reduce the efficiency of the illumination system and cause the area illuminated thereby to take on the colors of the filtered light.

There is a need therefore for an improved solid-state flat-panel area-emitting lighting apparatus that provides an aesthetically pleasing environment and a usable, broadband illumination.

SUMMARY OF THE INVENTION

In one aspect of the invention, a solid-state area illumination system is provided. The illumination system comprises: a plurality of OLED devices each device formed on a separate substrate and each device emitting light at a plurality of angles relative to the substrate, the emitted light having different ranges of frequencies at different ranges of the plurality of angles; and a support positioning each of the plurality of OLED devices at a plurality of orientations relative to an area of illumination, the positioning being defined so that any point on any surface within the area of illumination will receive a broadband combination of light from more than one of the OLED devices.

In another aspect of the invention, a solid-state illumination system is provided that comprises: a plurality of OLED devices each device formed on a separate substrate and each device emitting light at a plurality of angles relative to the substrate, the emitted light having different ranges of frequencies at different ranges of the plurality of angles; with each OLED device including a first electrode formed over the substrate and a second electrode with at least one of the first electrode and second electrode having a surface that is at least partially reflective and having at least one layer of light emitting organic material formed between the first electrode and second electrode, the at least one light emitting organic material layer emitting light at a plurality of angles relative to the normal of the at least one layer of organic material; wherein the electrodes and the at least one layer of organic material are formed so that the distance that emitted light travels from the light emitting layer to the at least one partially reflective surface varies depending on the angle of emission so that the frequency of light emitted from the OLED device to an illuminated surface depends upon the emission angle. A support positions the plurality of OLED devices at a plurality of orientations relative to an area of illumination, the positioning being defined so that any illuminated point on any surface within the area of illumination will receive a substantially common broadband combination of light from more than one of the plurality of OLED devices.

In yet another aspect of the invention, a method of forming a solid-state illumination system is provided. The illumination system comprises the steps of: forming a plurality of OLED devices on separate substrates, each device emitting light at a plurality of angles relative to the substrate, the emitted light having different ranges of frequencies at different ranges of the plurality of angles; and providing a support for positioning the plurality of OLED devices at a plurality of orientations relative to an area of illumination, the positioning being defined so that any point on any surface within the area of illumination will receive a generally homogeneous broadband combination of light from more than one of the OLED devices.

ADVANTAGES

The present invention has the advantage of providing a solid-state flat-panel decorative color lamp providing white-light illumination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one embodiment of a solid-state illumination assembly;

FIG. 2 illustrates a partial cross section of one embodiment of an OLED device;

FIG. 3 illustrates surface illumination made by one embodiment of a solid-state illumination system;

FIG. 4 is a perspective view of an embodiment of a solid-state illumination system;

FIG. 5 is a perspective view of an alternative embodiment of the present invention;

FIG. 6A illustrates a pattern of reflection within one embodiment of an OLED device;

FIG. 6B illustrates a pattern of reflection within one embodiment of a plurality of OLED devices; and

FIG. 7 illustrates a prior-art embodiment of an area illumination system.

It will be understood that the figures are not to scale since the individual layers are too thin and the thickness differences of various layers too great to permit depiction to scale.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1,2, and5, one embodiment of a solid-state area illumination system is illustrated. In the embodiment ofFIG. 1, solid-state illumination system6 comprises a plurality ofOLED devices8, eachOLED device8 is formed on aseparate substrate10. EachOLED device8 has afirst electrode12 formed over thesubstrate10 with one or more layers oforganic material14 formed or otherwise provided on thefirst electrode12 and with asecond electrode16 formed or otherwise provided over the one or more layers oforganic material14. In the embodiment illustrated, anencapsulating cover20 is provided as an outer layer. Theorganic material14 emits light (21,22,23) at a plurality of angles relative tosubstrate10. The emitted light has different ranges of frequencies at different ranges of the plurality of angles. The frequency of light emitted depends on the angle of emission with respect tosubstrate10. As shown in the example embodiments ofFIGS. 3,4 and5, asupport50 positions the plurality ofOLED devices8 at a plurality of orientations relative to an area ofillumination40. The positioning is such that anypoint32 on anyilluminated surface30 within area ofillumination40 will receive a broadband combination of different frequencies of light from more than one of the plurality ofOLED devices8. As used herein, broadband light is any light that combines two discernibly different colors of light. The broadband light can be generally white in appearance and may have a desired white point or color rendition index (CRI). If desired, the broadband light can also have a colored appearance.

Referring toFIG. 2, upon application of avoltage18 acrosselectrodes12 and16, current flows throughorganic material14 andorganic material14 emits light. Either or both thesubstrate10 andcover20 can be transparent or otherwise less than fully opaque, while at least one of thefirst electrode12 andsecond electrode16 can be at least partially transparent to allow light emitted byorganic material14 to escape fromOLED device8. Depending on which electrode is at least partially transparent and on the extent of transparence of thesubstrate10 orcover20, light will be emitted through either or bothsubstrate10 and cover20. If only one electrode is partially transparent or transparent, the other electrode is typically reflective.

The frequency of light emitted from eachOLED device8 has a dependence on the angle of emission that can be created by any of a variety of techniques. For example, such angular dependence can be created by forming a one-dimensional or a two-dimensional grating, a photonic crystal structure, and/or a surface plasmon structures on one of the electrodes. Diffraction gratings have been proposed to control the attributes of light emission from thin polymer films by inducing Bragg scattering of light that is guided laterally through the emissive layers; see “Modification of Polymer Light Emission by Lateral Microstructure” by Safonov et al., Synthetic Metals 116, 2001, pp. 145-148, and “Bragg Scattering from Periodically Micro-structured Light Emitting Diodes” by Lupton et al., Applied Physics Letters, Vol. 77, No. 21, Nov. 20, 2000, pp. 3340-3342. U.S. Pat. No. 6,670,777 issued Dec. 30, 2003 describes a surface plasmon method for improving light output. These techniques typically rely upon a reflective electrode having a surface with a variable distance from a transparent or semi-reflective electrode.

OLED devices8 that use micro-cavity structures also emit light at a plurality of angles with the emitted light having a frequency that depends upon the angle of emission, see for example U.S. Pat. No. 6,680,570 issued Jan. 20, 2004 and “Sharply Directed Emission in Organic Electroluminescent Diodes with an Optical-Microcavity Structure” by Tsutsui et al., Applied Physics Letters 65, No. 15, Oct. 10, 1994, pp. 1868-1870. This technique relies upon a reflective electrode and a semi-reflective electrode. Referring toFIGS. 6A and 6B, what is shown is one embodiment of anOLED device8 that uses a microcavity structure and can comprise, for example, areflective electrode16; asemi-reflective electrode12 with one or more layers of light emittingorganic material14 formed between the reflective and semi-reflective electrodes, the light emitting organic material being operable to emit light at a plurality of angles relative to the normal of the one or more layers of organic material. In this example,electrodes12,16 andorganic material14 are arranged to cause emitted light to travel a distance fromorganic material14 to the at least partially reflective surface that varies based upon the angle of emission. For example, referring toFIG. 6A,light ray21 is emitted inlayer14 and reflects between the reflective andsemi-reflective electrodes16 and12 before it passes throughelectrode12 and is seen by aviewer60. Points Al and A2 on the two electrodes illustrate the path oflight ray21 and define the length of the optical cavity and, hence, the frequency of the light emitted. Similarly, the optical cavity corresponding tolight ray22 is illustrated with points B1 and B2. Since the distance between B1 and B2 is different from the distance between A1 and A2, the frequency of light seen by theviewer60 will likewise differ. This difference will be largest if theOLED device8 is very close toviewer60 andlight ray21 is emitted nearest theviewer60 andlight ray22 is emitted farthest from theviewer60. This arrangement however, is not well-suited for providing broadband illumination over an area of illumination that can extend over a range of distances fromOLED device8. In the embodiment illustrated inFIG. 6B,OLED devices8 are positioned at different angles. This difference in angle creates a difference in optical cavity length and causes the frequency of the light radiated by the OLED devices to vary based upon the angular orientation of theOLED devices8. For example,light ray21 may be blue, whilelight ray22 may be green or red. The extent of the color shift is dependent upon structural features ofOLED device8 including, but not limited to, the extent of the separation betweenelectrodes12 and16, the reflectivity ofelectrodes12 and16 in microcavity type OLED devices, theOLED material14 layer thicknesses, and the arrangement of grating structures, polytonic crystal structures and/or surface plasmon structures used in conjunction with OLEDs. Similarly, it will be appreciated that the selection of materials used inOLED devices8 can impact the extent of the color shift variation. It will also be appreciated that such factors can also influence the overall set of frequencies of light emitted by an OLED device, such that the set of frequencies of light emitted by any one of the plurality ofOLED devices8 used in anillumination device6 can differ from the set emitted byother OLED devices8. For example, someOLED devices8 can emit a broader range of frequencies of light than others.

In prior-art OLED devices, this angular dependence effect is detrimental to the performance of a display or illumination device and is defeated through scattering layers or careful optimization of layers in the device to minimize the effect. However, in the present invention, this effect is employed to useful effect. Means to create such effects employing microcavities are also described in U.S. Application Publication Nos. 2004/0149984 filed Jan. 31, 2003 in the names of Tyan et al., entitled “Color OLED Display with Improved Emission”; U.S. 2004/0140757 filed Jan. 17, 2003 in the names of Tyan et al., entitled “Microcavity OLED Devices”; U.S. 2005/0073228 filed Oct. 7, 2003 in the names Tyan et al., entitled “White-Emitting Microcavity OLED Device”; U.S. Pat. No. 6,917,159 filed Aug. 14, 2003 in the names of Tyan et al., entitled “Microcavity OLED Device”, and references found therein.

Referring toFIG. 7, a prior-art illumination system200 using asingle OLED device8 is illustrated being positioned at a distance from an illuminatedsurface30 and emits colored light of one frequency to apoint34 on the illuminatedsurface30 vialight ray21aand colored light of another frequency to adifferent point36 on the illuminatedsurface30 vialight ray21b. Althoughlight rays21aand21bare not emitted at precisely the same angle from the substrate of OLED device8 (and similarly forlight rays22aand22billuminating point36), because the substrate of theOLED device8 is relatively small with respect to the distance from theOLED device8 topoints34 or36 on illuminatedsurface30, all of the light rays emitted from theOLED device8 that are directed toward a common point will be very nearly parallel so that thepoints34 and36 on the illuminatedsurface30 will each be illuminated with light of a particular, nearly identical color. Hence, a practical prior-art illumination system200 using asingle OLED device8 will not provide broadband illumination on asingle point34 or36 on the illuminatedsurface30. Accordingly, as is described above, various prior-art methods have been developed to help reduce the angular variation of light from a single OLED device and to employ a white-light emittingorganic materials14 in the OLED device.

Referring again toFIGS. 1 and 3, anillumination system6 provides a generally more homogeneous broadband light to all points within area ofillumination40 without use of the prior-art methods. The illuminatedpoint32 is illuminated from at least twodifferent OLED devices8 oriented at different angles with respect to thepoint32. As used herein, oriented at different angles means that a normal to the illuminated surface forms different angles with respect to the normal of at least one of theOLED devices8, whether the normals are in the same plane or not. Although the preponderance of the light from any one of theOLED devices8 may be emitted at approximately the same angle and have approximately the same frequency due to the distance betweenOLED device8 and illuminatedpoint32, as illustrated inFIG. 7, at least a second one of the plurality ofOLED devices8 will be at a different angle and will therefore illuminatepoint32 with a different color. The combination of colors, particularly if many OLED devices are employed at different angles, will illuminate surfaces within an area ofillumination40 with a more acceptable, broadband, illuminating light. Thus, while the color of light from anyparticular OLED device8 received at any point in area ofillumination40 will likely be within a narrow range of color, such light will be combined with light from other ones of the plurality of OLED devices to form a broadband illuminating light that appears to be more homogeneous throughout area ofillumination40.

In addition to forming a broadband illuminating light, theOLED devices8 when viewed individually from any angle will be colored, since the light from anysingle point38 on theOLED device8 viewed from any illuminated point within area ofillumination40 will have a single color. Moreover, the color seen at each point on eachOLED device8 will change as the viewer moves, providing an aesthetic and dynamic rainbow light effect. Effectively, at any given illuminated point within the area ofillumination40, eachOLED device8 appears to be largely one color defined by the angle of the OLED device with respect to the illuminatedsubstrate30. While, in combination,multiple OLED devices8 oriented at different angles that will emit different colors of light onto a single point and the multiple different colors will combine to provide a generally common range of broadband illumination of objects within area ofillumination40.

Such broadband light can comprise a multi-frequency combination of light that forms a generally white light or that forms any other desired combination of colors to provide a desired color temperature or CRI or to colorize the area of illumination.

OLED devices8 may be constructed with an organic material that emits a narrowband light, for example green. Alternatively, theOLED devices8 may be constructed with one or more layers oforganic material14 that emit a broadband light, for example white. The angular dependence can be achieved for both narrowband and broadband organic emitters by carefully structuring the optical elements of the OLED, for example by optimizing the distance between theelectrodes12,16.Different OLED devices8 can be arranged bysupport50 at different angles and can have somewhat different ranges of colors emitted at different angles of emission to optimize the overall color of light output and the aesthetic effect of the OLED lamp. Applicants have for example, constructed both narrow-band and broadband light emitting OLED devices having a strong color dependence on angle of emission, for example from red to cyan.

It will be appreciated thatsupport50 can arrangeOLED devices8 in a variety of fashions. For example,FIG. 1 illustrates one embodiment of a solid-state illumination system6 havingOLED devices8 that are not in a common plane and that have normals that are at an angle to each other, as well as to the illuminatedpoint32 on thesurface30. In contrast,FIG. 3 illustrates an alternative embodiment, whereinOLED devices8 are in a common plane and have normals that are parallel to each other. However, becauseOLED devices8 are located over an extended area whose size is comparable to, or smaller than, the distance from the common plane to illuminatedsurface30, OLED devices are oriented at more than one different angle with respect to illuminatedpoint32 onsurface30. This kind of arrangement may be found, for example, in a large room with solid-state illumination system6 mounted in the ceiling where the size of the floor and ceiling is much larger than the height of the ceiling from the floor.

Other embodiments ofsupport50 are illustrated inFIGS. 4 and 5 which illustrate by way of example only other embodiments ofOLED devices8 in solid-state illumination system6 mounted at a variety of orientations in other supports50.Supports50 of the types illustrated inFIGS. 4 and 5 can be, for example, part of a floor lamp, table lamp, or ceiling mounted lamp such as a chandelier. Likewise,illumination system6 may be employed for room lighting and the illuminatedsurface30 may be, for example and not by way of limitation, a floor, wall, and/or ceiling. Additional light-controlling elements may be employed withillumination system6, for example lumieres and shades. According to the present invention, the plurality ofOLED devices8 will be mounted at a variety of angles with respect to an illuminated point. It is preferred that the angle of the OLED device substrate normal also vary with respect to the illuminated substrate, since a plurality of different frequencies are required to illuminate a point to provide a broadband illumination. To provide such variation, it is preferred to provide an angular variation of at least 30% between the normal of at least two of theOLED devices8, since the optical cavity length will vary with the inverse of the cosine of the angle. A variation of at least 60% between the normal of at least two of the OLED devices provide a wider frequency variation, for example up to a factor of 2. Note that the actual color variation will depend not only on the color of light emitted at a normal to the OLED device but also on the optical cavity modes.

In various embodiments of the present invention, anOLED device8 may emit green-colored light in a direction normal to the OLED device. Alternatively, red, or blue light may be emitted, or other colors such as yellow or cyan. In other embodiments, the plurality of OLED devices may emit a plurality of different colors normal to theOLED device8. Different colors of emission may be provided by employingdifferent OLED materials14 in the various OLED devices.

Substrate10 and/or cover20 ofOLED device8 may be rigid and made of glass or other rigid materials such as metal sheets. Alternatively,substrate10 and/or cover20 ofOLED device8 may be flexible and made of plastic or metal foil or other flexible materials. In some embodiments of the present invention, one ormore OLED devices8 may comprise atransparent substrate10 andtransparent cover20 and may emit light from both sides of the OLED device. One or more of theOLED devices8 may be either top- or bottom-emitting OLED devices. Means for manufacturing OLED devices in these configurations are known in the art.

A solid-state illumination system6, such as the one described above inFIG. 1, can be made, for example, by forming a plurality of OLED devices on separate substrates, each OLED device emitting light at a plurality of angles relative to the substrate, said emitted light having different ranges of frequencies at different ranges of the plurality of angles; and providing a support for positioning the plurality of OLED devices at a plurality of orientations relative to an area of illumination, the positioning being defined so that any point on any surface within the area of illumination will receive a generally homogeneous broadband combination of light from more than one of the OLED devices.

In one embodiment, the invention is employed in an area illumination device that includes an Organic Light Emitting Diode (OLED) which is composed of small molecule or polymeric OLED materials as disclosed in, but not limited to, U.S. Pat. No. 4,769;292, issued Sep. 6, 1988 to Tang et al., and U.S. Pat. No. 5,061,569, issued Oct. 29, 1991 to VanSlyke et al. The light source may also include multiple light emitting layers as described in commonly assigned U.S. Application Publication No. 2003/0170491 filed Feb. 15, 2002 by Liao et al., the disclosure of which is incorporated herein by reference.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

PARTS LIST

• 6 solid-state area of illumination system
• 8,8a,8bOLED device
• 10 substrate
• 12 electrode
• 14 organic light emitting layer
• 16 electrode
• 18 power source
• 20 encapsulating cover
• 21,21a,21blight rays
• 22,22a,22blight rays
• 23,23a,23blight rays
• 24,24a,24blight rays
• 25,25a,25blight rays
• 30 illuminated surface
• 32 illuminated point
• 34 illuminated point
• 36 illuminated point
• 40 illuminated area
• 50 fixture
• 60 viewer
• 200 illumination system

Claims (15)

1. A solid-state illumination system for illuminating an area with white light comprising:

a plurality of OLED devices, each OLED device formed on a separate substrate having a light-emitting area and each OLED device emitting light at a plurality of angles relative to the substrate in the light-emitting area, said emitted light having different ranges of frequencies at different ranges of the plurality of angles, wherein each different range of frequencies corresponds to a single, different color emitted at each of the different ranges of angles over the substrate light-emitting area; with each OLED device including a first electrode formed over the substrate and a second electrode that in each OLED has a single, fixed distance from the first electrode over the substrate light-emitting area with at least one of the first electrode and second electrode having a surface that is at least partially reflective and having at least one layer of an unpatterned, common light emitting organic material formed between the first electrode and second electrode, said at least one light emitting organic material layer emitting light at a plurality of angles relative to the normal of at least one layer of organic material;

wherein the electrodes and the at least one layer of organic material are formed so that the distance that emitted light travels from the light emitting layer to the at least one partially reflective surface varies depending on the angle of emission so that the frequency of light emitted from the OLED device substrate light-emitting area to an illuminated surface depends upon the emission angle; and

a support positioning the plurality of OLED devices at a plurality of orientations relative to an area of illumination, said positioning being defined so that any illuminated point within the area of illumination will receive a substantially common broadband combination of light selected to form white light from more than one of the plurality of OLED devices.

2. The solid-state area illumination system ofclaim 1, wherein the plurality of OLED devices are not located in a common plane.

3. The solid-state area illumination system ofclaim 1, wherein the plurality of OLED devices are located in a common plane.

4. The solid-state area illumination system ofclaim 1, wherein the illumination system is a chandelier, a table lamp, or a floor lamp.

5. The solid-state area illumination system ofclaim 1, wherein the illuminated surface is a floor, wall, ceiling, or item of furniture.

6. The solid-state area illumination system ofclaim 1, wherein at least one substrate is a rigid planar substrate.

7. The solid-state area illumination system ofclaim 1, wherein at least one substrate is flexible.

8. The solid-state area illumination system ofclaim 1, wherein at least one OLED device comprises a transparent substrate and transparent cover and light is emitted from both sides of the OLED device.

9. The solid-state area illumination system ofclaim 1, wherein the OLED devices emit broadband light.

10. The solid-state area illumination system ofclaim 1, wherein the OLED devices emit a single color of light in a direction normal to the surface of the substrate.

11. The solid-state area illumination system ofclaim 10, wherein the singe color of light emitted in a direction normal to the surface of the substrate is red, green, blue, yellow or cyan.

12. The solid-state area illumination system ofclaim 10, wherein the OLED devices are microcavity devices.

13. The solid-state area illumination system ofclaim 10, wherein at least one OLED device is a top-emitting OLED device.

14. The solid-state area illumination system ofclaim 10, wherein at least one OLED device is a bottom-emitting OLED device.

15. The solid-state area illumination system ofclaim 1, wherein at least two of the OLED devices radiate light at a different range of frequencies.

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